Recent developments in the field of p-conjugated polymers have led to considerable improvements in the performance of solution-processed organic light-emitting devices (OLEDs). However, further improving efficiency is still required to compete with other traditional light sources. Here we demonstrate efficient solution-processed multilayer OLEDs using small molecules. On the basis of estimates from a solvent resistance test of small host molecules, we demonstrate that covalent dimerization or trimerization instead of polymerization can afford conventional small host molecules sufficient resistance to alcohols used for processing upper layers. This allows us to construct multilayer OLEDs through subsequent solution-processing steps, achieving record-high power efficiencies of 36, 52 and 34 lm W À 1 at 100 cd m À 2 for solution-processed blue, green and white OLEDs, respectively, with stable electroluminescence spectra under varying current density. We also show that the composition at the resulting interface of solution-processed layers is a critical factor in determining device performance.

We report the application of two surface modifiers, 2-(2-hydroxyphenyl)benzothiazole (BTz) and 8-quinolinol (8Qn), to electron-transporting layers (ETLs) comprising zinc oxide nanoparticles (ZnO NPs) to improve the efficiency of electron injection into light-emitting layers in organic light-emitting devices (OLEDs). BTz and 8Qn were respectively added to ZnO NP dispersions; these surface modifiers then reacted with the ZnO NPs and changed their optical properties, proving the interaction between the ZnO NPs and modifiers. The modified ZnO NPs were employed as ETLs in fluorescent polymer-based OLEDs. The BTz-device showed a slightly lower driving voltage and a slightly higher luminous efficiency than the unmodified ZnO device, whereas the 8Qn-device showed a much lower driving voltage and a much higher luminous efficiency than the unmodified ZnO device. The device driving stability was evaluated, and both of the modified devices showed improved lifetimes compared with the unmodified device. In particular, a more than five-fold improvement in lifetime was obtained for the BTz-device.

For the practical application of organic light emitting devices (OLEDs) based on thermally activated delayed fluorescence (TADF) for large area TV and solid state lighting, low power consumption as well as the operation lifetime at high brightness over 1000 cd m must be improved. Here, we have developed a novel hexaphenylbenzene-based sterically bulky hole-transport layer named 4DBTHPB with deep ionization potential of 5.8 eV and high triplet energy of 2.7 eV. By using 4DBTHPB, we can realize a highly efficient and stable TADF OLED exhibiting external quantum efficiency of 21.6 % and power efficiency of 54.3 lm W and operation lifetime at 50 % (LT ) of approximately 10 000 h at an initial luminance of 1000 cd m . These performances are comparable to those of the state-of-the-art green phosphorescent OLEDs reported in the scientific literatures.

The solution-processable host material, 3,3¤-[bis(9-phenylcarbazol-3-yl)]benzophenone (BCzBP), containing donor-type phenylcarbazole units and an acceptor-type benzophenone unit was synthesized. BCzBP showed a high excited triplet energy level and a high photoluminescence quantum efficiency with tris[2-(4-tolyl)pyridine]iridium ([Ir(mppy) 3 ]) as a dopant, and a high glass-transition temperature. Solution-processed green phosphorescent OLEDs were fabricated with BCzBP. The device with BCzBP as a host showed comparable efficiencies to those of the corresponding device with 4,4¤-bis(N-carbazolyl)biphenyl (CBP) as a host. At the same current density, the device with BCzBP showed a longer device lifetime than that with CBP, due to the high thermal stability and the bipolar nature of the host compound, BCzBP.Solution-processed organic light-emitting devices (OLEDs) are considered essential for the next generation of low-cost and large-area flat-panel displays and lighting sources. 16 Phosphorescent compounds are effective to improve the efficiency of the device, compared with fluorescent materials. 7,8 However, it is rather difficult to achieve a long lifetime in phosphorescent OLEDs, and the solution process makes it more difficult. 9,10 The host materials for solution-processed phosphorescent OLEDs require high energy level of excited triplet state (T 1 ) not to quench triplet exciton of the phosphorescent emitter, chargetransporting ability for low driving voltage, high glass-transition temperature (T g ) for long lifetime and less vulnerable to heat damage in OLEDs, bipolar property for electrochemical stability of cation radical and anion radical states, and good solubility in organic solvents for solution processability. 1114 In this study, we report a unique molecular design of combining phenylcarbazol as electron-donor unit and benzophenone as electron-acceptor unit to give a novel bipolar host material of 3,3¤-[bis(9-phenylcarbazol-3-yl)]benzophenone (BCzBP). The compound exhibited high T 1 and high T g . Solution-processed green phosphorescent OLEDs using an emitter of tris[2-(4-tolyl)phenylpyridine]iridium ([Ir(mppy) 3 ]) showed high external quantum efficiency (EQE) of 9.8% and a long half-lifetime of 365 h at a practical brightness of 1000 cd m ¹2 .The bipolar host material, BCzBP was readily synthesized by the Pd(0)-catalyzed SuzukiMiyaura cross-coupling reaction of two equivalents of 9-phenylcarbazole-3-boronic acid with 3,3¤-dibromobenzophenone (Scheme 1). The chemical structure was identified by 1 H-and 13 C NMR, mass spectrometry, and elemental analysis. The compound was thoroughly purified by train sublimation and the purity was higher than 99.9%, determined by high-performance liquid chromatography (HPLC) analysis. The thermal properties of BCzBP were investigated using thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC). The decomposition temperature (T d , corresponding to 5% weight loss) was 487°C, and T g was 116°C. The much higher T d and T g at 373°C and 62°C of 4...

Neutral zinc porphyrin containing flexible alkyl linker, 5-[4-(5-hydroxypentyloxy)phenyl]-10,15,20-tri-p-tolylporphyrinatozinc, was attached to the 5′ ends of 20- and 30-bp oligodeoxynucleotides (ODN) by solid-phase synthesis. Zinc porphyrin-modified double-stranded DNA (dsDNAs), which included dsDNAs with porphyrin moieties on one end and on both ends (ZnPor–ds20, ds20–ZnPor, ZnPor–ds20–ZnPor, ZnPor–ds30, ds30–ZnPor, and ZnPor–ds30–ZnPor), were successfully prepared and were analyzed by variable-temperature UV–vis spectroscopy and CD measurements to elucidate the interaction behavior of the porphyrin ring. Detailed investigation revealed that the zinc porphyrin–DNA conjugates exhibited intra-duplex porphyrin–ODN interaction in a low-salt condition and inter-duplex porphyrin–porphyrin interaction in a high-salt condition.